1. Field of the Invention
This invention relates to a control apparatus for an internal combustion engine, wherein a fuel injection quantity calculated by fuel-injection-quantity calculation means is corrected with purge-air-concentration learnt value which has been calculated by subjecting a purge air concentration to purge-air-concentration filtering, and wherein fuel in the corrected fuel injection quantity is injected from an injector.
2. Description of the Related Art
There has heretofore been known a vaporized-fuel processing device wherein vaporized fuel produced within the fuel feed system of an internal combustion engine, e. g., within a fuel tank is adsorbed and stored in a vaporized-fuel adsorption device (hereinbelow, termed the “canister”) and is thereafter introduced into the suction system of the engine together with air, thereby to purify (hereinbelow, expressed as “purge”) the canister.
Such a vaporized-fuel processing device has been as stated below. A purge valve is driven so as to realize a target purge air quantity which is set in accordance with the running state of the engine. When the vaporized fuel adsorbed in the canister has been introduced into the suction system together with the air, a deviation develops between an air/fuel ratio being a control target and an actual air/fuel ratio in accordance with the concentration of the vaporized fuel in the purge air. Therefore, a fuel injection quantity is corrected by an air/fuel ratio feedback control so as to bring the actual air/fuel ratio near to the air/fuel ratio being the control target. On this occasion, the purge air concentration is calculated from an actual purge rate and the correction magnitude of the air/fuel ratio feedback control, a purge-air-concentration learnt value is calculated by subjecting the calculated purge air concentration to filtering, and the fuel injection quantity is further corrected in accordance with the actual purge rate and the purge-air-concentration learnt value.
Besides, JP-A-8-261038 discloses a technique wherein the purge air concentration calculated from the purge rate and the air/fuel-ratio-feedback correction coefficient is subjected to the filtering, thereby to calculate the purge-air-concentration learnt value, and wherein when the purge air concentration has been calculated for the first time after the start of the internal combustion engine, the calculated result is not subjected to the filtering, but it is directly set as the purge-air-concentration learnt value, whereby the purge air concentration is calculated accurately and promptly.
Such prior-art vaporized-fuel processing devices for the engine, however, have had problems as stated below. First, as the actual behavior of the purge air concentration, after the start, the purge introduction is done in the state of a thick purge air concentration because the vaporized fuel in a large quantity is held adsorbed in the canister. As the purge introduction proceeds in accordance with the running state, the purge air concentration changes in the direction of thinning from the thick state, while fluctuating in accordance with a purge flow rate. (Refer to (a) in FIG. 9.) When the purge introduction has proceeded to some extent, to decrease the vaporized fuel adsorbed in the canister, the purge air concentration becomes thin. Therefore, the changes of the purge flow rate do not conspicuously appear in the purge air concentration changes, and the purge air concentration changes gently. Besides, in the case where the purge air concentration is thin, the calculation of the purge air concentration is more susceptible to disturbances (such as air/fuel ratio fluctuations ascribable to an acceleration and a deceleration) other than the purge, and the errors of the purge-air-concentration calculation become large. (Refer to (b) in FIG. 9.)
Meanwhile, with the prior art stated in JP-A-8-261038, in the case where the purge air concentration has been calculated for the first time after the start of the internal combustion engine, without considering the changing situation of the purge air concentration, the calculated result is not subjected to the filtering and is directly set as the purge-air-concentration learnt value. Thereafter, the purge air concentration is subjected to the filtering with a predetermined fixed filter constant, thereby to calculate the purge-air-concentration learnt value.
Here, in filtering the calculated result of the purge air concentration and calculating the purge-air-concentration learnt value, the filter constant which can absorb the purge-air-concentration calculation errors ((c) in FIG. 9) having developed in the case where the purge air concentration is thin and changes gently is set by way of example. Then, the purge-air-concentration fluctuations ((d) in FIG. 9) ascribable to the purge-flow-rate changes are also absorbed, and an accurate purge-air-concentration learnt value cannot be calculated ((e) in FIG. 9). Therefore, the air/fuel ratio cannot be maintained at the target air/fuel ratio (for example, a theoretical air/fuel ratio), resulting in the problem that an exhaust gas worsens.